1. Field of the Invention
The present invention relates to tilt detection system, tilt detection method and tilt adjustment method in an optical disk drive for detecting/adjusting a tilt of a light beam with respect to a disk recording surface.
2. Description of the Related Art
A light beam emitted from a semiconductor laser is incident on a recording surface of an optical disk at right angles through an objective lens for reading a signal recorded on the optical disk. However, when the light beam is not incident on the recording surface of the optical disk at right angles due to inclination of the optical disk and/or inclination of the objective lens, coma aberration is generated. As the coma aberration increases, the cross talk increases, and the S/N ratio of the read signal is degraded. Thereby, distortion occurs in the reproduced waveform, and jitter occurs, as is well known.
Therefore, in order to adjust the tilt of light beam with respect to the optical disk, ordinarily, the jitter amount of the RF waves reproduced from the optical disk is measured for radial direction and tangential direction of the optical disk (hereinafter, the term xe2x80x98of the optical diskxe2x80x99 in xe2x80x98radial/tangential direction of the optical diskxe2x80x99 being omitted) separately, with the optical disk in the reproduced condition, and the respective tilts are adjusted so that the jitter amount becomes minimum. This adjustment may be made as a result of the pickup of the optical disk drive being inclined or as a result of the spindle motor of the optical disk drive being inclined.
FIGS. 1A and 1B show the jitter amount of the reproduced RF signal with respect to the tilt in radial direction and the jitter amount of the RF signal with respect to the tilt in tangential direction, respectively, at the time of tilt adjustment. The jitter amount is minimum when the tilt is 0, and the jitter amount increases as the tilt increases. The inclination of the pickup or spindle motor for radial direction and tangential direction is adjusted, where the state (inclination) of the pickup or spindle motor in which the jitter amount is minimum is regarded as the optimum state in tilt adjustment.
As shown in FIG. 1B, change in jitter amount with respect to the tilt in tangential direction is steep about the point at which the tilt is 0. Accordingly, it is easy to find the optimum state in tilt adjustment, and, thus, to adjust the tilt optimally. However, as shown in FIG. 1A, change in jitter amount with respect to the tilt in radial direction is gentle about the point at which the tilt is 0. Accordingly, it is difficult to find the optimum state in tilt adjustment, and, thus, to adjust the tilt optimally.
An object of the present invention is to provide a tilt detection system by which it is possible to easily detect the optimum state in tilt adjustment also for radial direction similarly to the case for tangential direction, and to perform the tilt adjustment precisely and easily.
Tilt detection according to the present invention comprises:
recording in an optical disk a series of data recorded, the series of data having a pulse width smaller than the minimum pulse width of data recorded in an ordinary optical disk;
reproducing a signal from the optical disk by emitting a light beam onto the optical disk; and
detecting a tilt of the light beam with respect to the optical disk based on a reproduced RF signal provided by the reproducing part when the series of data having the smaller pulse width is reproduced.
In this configuration, as a result of a signal being reproduced from an optical disk in which information inverts faster than data having the minimum pulse width recorded in an ordinary optical disk, the quality of the recorded data is degraded, and the quality of the reproduced signal sensitively responds to, change in the tilt. Accordingly, even in radial direction, it is easy to detect the optimum state in tilt adjustment similarly to the case of tangential direction, and thus to perform the tilt adjustment precisely and easily.
Tilt detection according to another aspect of the present invention comprises:
reproducing a signal from the optical disk;
decreasing a gain of a low-pass filter limiting a for the highest frequency of predetermined essential frequencies of a reproduced RF signal obtained from the reproduction the signal from the optical disk; and
detecting a tilt based on the signal having the above-mentioned highest frequency having passed the low-pass filter.
In this configuration, the low-pass filter limits the frequency band of the signal obtained through reproducing, and decreases the amplitude of the signal of the above-mentioned highest frequency of the signal obtained through the reproduction. Thereby, the quality of the signal in of the highest frequency is degraded, and the quality of the reproduced signal sensitively responds to change in the tilt. Accordingly, even in radial direction, it is easy to detect the optimum state in tilt adjustment similarly to the case of tangential direction, and to perform the tilt adjustment precisely and easily.
Tilt detection according to another aspect of the present invention comprises:
reproducing at a speed higher than an ordinary speed a signal from an optical disk having data recorded therein in an ordinary recording density; and
detecting the tilt based on a reproduced RF signal obtained through the reproduction.
In this configuration, data of the optical disk in which recording is made at an ordinary speed is reproduced at a speed higher than the ordinary speed. Thereby, the quality of the signal is degraded, and the quality of the reproduced signal sensitively responds to change in tilt. Accordingly, even in radial direction, it is easy to detect the optimum state in tilt adjustment similarly to the case of tangential direction, and to perform the tilt adjustment precisely and easily.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.